International application No. WO 97/27030 discloses a razor with a reversible blade unit, in order to extend the useful life of the blade unit.
The blade unit is engaged into a housing and is provided with turning knobs, located at either end of the blade unit. Upon the dulling of the cutting edges on one side of the blade unit, the user turns the knobs such that the dulled cutting edges are rotated to the rear of the housing while the still sharp, unused cutting edges are rotated such that they are exposed at the front of the housing and are then ready for use.
One disadvantage of such a razor is that, when the user wants to turns the knobs, his soapy hands might slip on the knobs, thereby preventing him from turning the blade unit in a single movement.
Another disadvantage of such a razor is that it is quite dangerous for the user, for as the knobs are thin and located near the blades, any wrong move might result in the user cutting his fingers.